The present invention relates to diamond sintered body tools and manufacturing methods thereof. More particularly, the present invention relates to a diamond sintered body tool having superior adhesion resistance, chipping resistance and strength as well as a manufacturing method thereof.
Since diamond sintered bodies have superior wear resistance and strength, they are widely used as tool materials in a field that requires strength and wear resistance such as the fields of cutting tools, drilling tools and wire drawn die tools. Such diamond sintered bodies are known, for example, as the one provided by filling diamond powder in a container made of a tungsten carbidexe2x80x94cobalt cemented carbide and sintering it at high temperature and under high pressure as described in Japanese Patent Publication No. 52-12126. Furthermore, Japanese Patent Laying-Open No. 54-114513 describes a diamond sintered body obtained by previously mixing diamond powder and iron group metal powder and maintaining the mixed powder at high temperature and under high pressure.
These diamond sintered bodies include an iron group metal such as cobalt as a sintering aid between sintered diamond particles.
As a diamond sintered body having improved heat resistance, the one in which an iron group metal is removed from the entire diamond sintered body is described in Japanese Patent Laying-Open Nos. 53-114589 and 7-156003.
However, when a conventional diamond sintered body including an iron group metal is used as a tool, cutting of a soft metal, especially an aluminum alloy, results in adhesion of the workpiece material on the cutting edge of the tool depending on the cutting conditions and thereby deteriorates the roughness of the finished surface of the workpiece material as well as the processing precision.
In a diamond sintered body from which an iron group metal is removed, the diamond sintered body includes a gap and has smaller strength, and therefore the diamond sintered body is easily chipped.
Therefore, the present invention was made to solve the above described problems, and its object is to provide a diamond sintered body tool capable of suppressing adhesion of a soft metal such as an aluminum alloy and having superior strength and chipping resistance.
The inventors conducted a study of adhesion of a workpiece material on the surface of a diamond sintered body tool when cutting an aluminum alloy. It was found out as a result that formation of a surface layer including at least one selected from silicon, a silicon oxide, a silicon carbide, a silicon nitride and a solid solution thereof on the surface of the diamond sintered body tool is remarkably effective for preventing adhesion of a workpiece material, which led to the present invention.
In other words, on the rake face or the flank face of a tool which is engaged in cutting, the diamond sintered body as a tool base material is in contact with the aluminum alloy and, under low cutting rate or dry cutting conditions, aluminum as a workpiece material adheres even on the surface of chemically stable diamond. This would be because the bond of aluminum and diamond on the surface of the diamond sintered body is relatively strong.
In contrast, if a surface layer including at least one selected from silicon (Si), a silicon oxide (SiO2), a silicon carbide (SiC), a silicon nitride (Si3N4) and a solid solution thereof is formed on the surface of the diamond sintered body tool, strongly bonded diamond and aluminum can be prevented from being in contact with each other and aluminum can be prevented from being adhered on the rake surface or the flank face of the tool because any of these surface layers are weakly bonded to aluminum.
Especially when the surface layer is formed of Si, SiO2, SiC or Si3N4, the bonding force of the surface layer and aluminum is lowered further since the surface layer is chemically stable, and the effect of preventing aluminum adhesion becomes higher.
The surface layer is generally formed in the following manner. When the surface layer is made of silicon, silicon powder having a particle size of at least 1 xcexcm and at most 20 xcexcm, for example, is pressed against the tool surface to form a thin silicon adsorption layer on the surface. When the surface is made of a silicon oxide, a silicon carbide and/or a silicon nitride, the surface layer is formed at a temperature of 400xc2x0 C. to 500xc2x0 C. using an arbitrary material gas selected from SiH4, O2, N2, C2H4 by the plasma CVD (Chemical Vapor Deposition) method, for example. Besides, the surface layer can also be formed by using similar material gases and the methods such as the vacuum deposition, sputtering and ion plating.
Thus, in order to bring about the effect of adhesion prevention, the thickness of the surface layer formed on the diamond sintered body needs to be at least 0.1 nm. when the thickness of the surface layer exceeds 1 xcexcm, formation of the surface layer often makes the surface rougher, which, on the contrary, easily causes adhesion of a workpiece material. Therefore, the thickness of the surface layer formed on the diamond sintered body is preferably in the range from 0.1 nm to 1 xcexcm.
When an iron group metal such as Fe, Co and Ni is used as a sintering aid in the diamond sintered body, the iron group metal tends to be a starting point of adhesion caused at the cutting edge of the tool since a good wetting property is observed between such iron group metals and aluminum. Although the xe2x80x9cwettabilityxe2x80x9d generally means easiness of contact between a solid and a liquid, it refers to easiness of close contact between a tool and a workpiece in this specification. Thus, xe2x80x9ca bad wettabilityxe2x80x9d indicates a situation when a tool and a workpiece come into contact, they do not closely contact each other. On the other hand, xe2x80x9ca good wettabilityxe2x80x9d indicates a situation when a tool and a workpiece come into contact, they tend to closely contact each other.
By previously removing an iron group metal included in the diamond sintered body from the surface and thereafter forming the surface layer, adhesion is effectively prevented even when the surface of the diamond sintered body is partially exposed by long term cutting.
In short, a diamond sintered body including an iron group metal is used to manufacture a tool, and then the tool is immersed in an acid solution to remove the iron group metal from the surface of the diamond sintered body. Then, a surface layer including at least one selected from silicon, a silicon oxide, a silicon carbide, a silicon nitride and a solid solution thereof is formed on the tool rake surface or the tool flank face of the diamond sintered body tool. Thus, adhesion resistance for long term cutting can be improved.
Similarly, a diamond sintered body including an iron group metal is immersed in an acid solution to remove the iron group metal from the surface of the diamond sintered body. Thereafter, the diamond sintered body is used to form a tool. By forming a surface layer including at least one selected from silicon, a silicon oxide, a silicon carbide, a silicon nitride and a solid solution thereof on the tool rake surface or the tool flank face of the tool, adhesion resistance for long term cutting can be improved.
Furthermore, a diamond sintered body including an iron group metal is immersed in an acid solution to remove the iron group metal from the surface of the diamond sintered body. Thereafter, a surface layer including at least one selected from silicon, a silicon oxide, a silicon carbide, a silicon nitride and a solid solution thereof is formed on the surface of the diamond sintered body. By forming a tool using it, adhesion resistance for long term cutting can be improved.
Here, the diamond sintered body in which the iron group metal is removed from the surface as described above is characterized in that it includes an inner portion including a first content of the iron group metal, and a surface portion surrounding the inner portion and including a second content of the iron group metal, the second content being lower than the first content. The sintered body structure is formed with such a changing content of the iron group metal because the cutting performance of the sintered body is to be improved when it is used as a tool.
That is, when the iron group metal is removed over the entire sintered body, the diamond sintered body includes a gap and has small strength and therefore the tool is easily chipped. In the present invention, since the iron group metal is removed only from the surface layer of the diamond sintered body, the strength of the sintered body is not lowered and the tool is not chipped. Therefore, adhesion resistance is effectively improved.
In order to obtain such an effect, the second content of the iron group metal needs to be at most 2.0% by weight. when the thickness of a sintered body surface portion having the second content is 2 nm or less, it is difficult to attain the effect of improving adhesion resistance by removing the iron group metal from the surface of the diamond sintered body. When the thickness of a sintered body surface portion having the second content exceeds 5000 nm, the cutting edge of the tool is easily chipped. Therefore, the range of thickness of the surface portion having the second content is preferably at least 2 nm and at most 5000 nm from the surface of the diamond sintered body. Particularly, in a preferred embodiment of the present invention, the particle size of diamond particles in the diamond sintered body is at least 0.1 xcexcm and at most 60 xcexcm, and the content of sintered diamond particles in the diamond sintered body is at least 80% and at most 96% by volume.
The inventors conducted various studies of adhesion of a workpiece material on the surface of a diamond sintered body tool when cutting an aluminum alloy. As a result, it was found out that adhesion of a workpiece material starts from an iron group metal (iron, cobalt, nickel) included in the diamond sintered body tool.
Since the iron group metal (cobalt, iron, nickel) used as a sintering catalyst in the diamond sintered body has a good wettability with respect to aluminum as a workpiece material, aluminum first comes into close contact with the iron group metal on the surface of the diamond sintered body tool. Thereafter, adhesion of aluminum spreads over the entire surface of the diamond sintered body tool as was found out.
Thus, in order to prevent adhesion, the iron group metal existing on the surface of the diamond sintered body tool is removed, and therefore the adhesion resistance of the diamond sintered body tool is substantially improved.
However, when the iron group metal is removed from the entire diamond sintered body as in conventional cases, a large number of gaps exist in the diamond sintered body, which causes the strength to be lowered and chipping to occur easily. Then, the present invention aims to prevent decrease in the strength and occurrence of chipping by removing the iron group metal only from the surface portion of the diamond sintered body tool.
A diamond sintered body tool of the present invention based on such an idea includes a tool base material including a diamond sintered body, and a surface layer including at least one material selected from the group of silicon, a silicon oxide, a silicon carbide, a silicon nitride and a solid solution thereof formed on a surface of the tool base material. The silicon oxide is preferably SiO2. The silicon carbide is preferably SiC. The silicon nitride is preferably Si3N4. The thickness of the surface layer is preferably at least 0.1 nm and at most 1 xcexcm. The diamond sintered body tool is preferably brazed to a tool original material. The tool base material has a tool rake surface and a tool flank face, and the surface layer is preferably formed on at least one of the tool rake surface and the tool flank face.
A diamond sintered body tool according to another aspect of the present invention includes a tool base material including a diamond sintered body, and a surface layer including at least one material selected from the group of silicon, a silicon oxide, a silicon carbide, a silicon nitride and a solid solution thereof formed on a surface of the tool base material. The tool base material has an inner portion including a first content of an iron group metal, and a surface portion surrounding the inner portion and including a second content of the iron group metal, the second content being lower than the first content. The silicon oxide is preferably SiO2. The silicon carbide is preferably SiC. The silicon nitride is preferably Si3N4. The thickness of the surface layer is preferably at least 0.1 nm and at most 1 xcexcm. The second content is preferably at most 2.0% by weight. A portion which is at least 2 nm and at most 5000 nm in depth from the diamond sintered body surface is preferably the surface portion. The diamond sintered body tool is preferably brazed to the tool original material. Preferably, the tool base material has a tool rake surface or a tool flank face, and the surface layer is formed on at least one of the tool rake surface and the tool flank face.
A diamond sintered body tool according to another aspect of the present invention includes an inner portion including a first content of an iron group metal, and a surface portion surrounding the inner portion and including a second content of the iron group metal, the second content being lower than the first content.
According to such a structure, the content of the iron group metal is low in the surface portion, and it becomes difficult for aluminum to be adhered on the surface portion. Since a larger amount of iron group metal exists in the inner portion than in the surface portion, occurrence of a gap in the inner portion can be suppressed. Therefore, the strength and the chipping resistance are not lowered.
The second content is preferably at most 2.0% by weight.
A portion which is at least 2 nm and at most 5000 nm in depth from the diamond sintered body tool surface is preferably the surface portion.
For a sintered body having a relatively lower diamond content in which the content of sintered diamond particles is at most 96% by volume, or for a sintered body in which the diameter of a sintered diamond particle is at most 60 xcexcm, adhesion of aluminum is particularly easily caused. Since the minimum size of an actually producible sintered diamond particle is 0.1 xcexcm and the diamond content in this case is 80% by volume, the effects of the present invention are particularly evident for a diamond sintered body tool in which the size of a diamond particle is at least 0.1 xcexcm and at most 60 xcexcm or the content of sintered diamond particles is at least 80% and at most 96% by volume.
The diamond sintered body tool is preferably brazed to a tool original material.
Furthermore, at least one of the tool rake surface and the tool flank face is preferably formed on the surface portion.
Adhesion of the above described workpiece made of an aluminum alloy is also greatly influenced by cutting conditions.
Especially in the case the cutting speed is under 200 m/min, adhesion easily occurs on the surface of the diamond sintered body tool. Therefore, for milling or drilling tools of which the cutting speed is lower, such as a reamer tool, an end mill tool, a drill tool and a boring tool, the present invention provides remarkable effects for adhesion resistance.
A method of manufacturing a diamond sintered body tool according to one aspect of the present invention includes the steps of (1) preparing a diamond sintered body, (2) processing the diamond sintered body to form a diamond sintered body tool, and (3) forming a surface layer including at least one selected from the group of silicon, a silicon oxide, a silicon carbide, a silicon nitride and a solid solution thereof on a surface of the diamond sintered body tool.
A method of manufacturing a diamond sintered body tool according to another aspect of the present invention includes the steps of (1) preparing a diamond sintered body including an iron group metal, (2) processing the diamond sintered body to form a diamond sintered body tool, and (3) surface treating the diamond sintered body tool by immersing the diamond sintered body tool in an acid solution to remove the iron group metal from a surface portion and thereby make the content of the iron group metal lower in the surface portion than in the inner portion.
The acid solution preferably includes at least one selected from the group of nitric acid, hydrochloric acid and hydrofluoric acid.
The content of iron group metal in the surface portion is preferably at most 2.0% by weight.
A method of manufacturing a diamond sintered body tool according to still another aspect of the present invention includes the steps of (1) preparing a diamond sintered body including an iron group metal, (2) surface treating the diamond sintered body by immersing the diamond sintered body in an acid solution to remove the iron group metal from a surface portion of the diamond sintered body and thereby make the content of the iron group metal lower in the surface portion than in an inner portion of the diamond sintered body, and (3) processing the surface treated diamond sintered body to obtain a diamond sintered body tool.
In these methods of manufacturing a diamond sintered body, the content of the iron group metal is made lower in the surface portion than in the inner portion, and therefore a diamond sintered body tool having superior adhesion resistance, strength and chipping resistance can be obtained.
A method of manufacturing a diamond sintered body tool according to a further aspect of the present invention includes the steps of (1) preparing a diamond sintered body including an iron group metal, (2) processing the diamond sintered body to form a diamond sintered body tool, (3) immersing the diamond sintered body tool in an acid solution to remove the iron group metal from a surface portion and thereby make the content of the iron group metal lower in the surface portion than in an inner portion, and (4) forming a surface layer including at least one selected from the group of silicon, a silicon oxide, a silicon carbide, a silicon nitride and a solid solution thereof on a tool rake surface or a tool flank face of the diamond sintered body tool.
The acid solution preferably includes at least one selected from the group of nitric acid, hydrochloric acid and hydrofluoric acid.
The content of the iron group metal in the surface portion is preferably at most 2.0% by weight.
A method of manufacturing a diamond sintered body tool according to a further aspect of the present invention includes the steps of (1) preparing a diamond sintered body including an iron group metal, (2) immersing the diamond sintered body in an acid solution to remove the iron group metal from a surface portion of the diamond sintered body and thereby make the content of the iron group metal lower in the surface portion than in an inner portion, (3) processing the surface treated diamond sintered body to obtain a diamond sintered body tool, and (4) forming a surface layer including at least one selected from the group of silicon, a silicon oxide, a silicon carbide, a silicon nitride and a solid solution thereof on a surface of the surface treated diamond sintered body tool.
The acid solution preferably includes at least one selected from the group of nitric acid, hydrochloric acid and hydrofluoric acid.
The content of the iron group metal in the surface portion is preferably 2.0% by weight.
A method of manufacturing a diamond sintered body tool according to a further aspect of the present invention includes the steps of (1) preparing a diamond sintered body including an iron group metal, (2) immersing the diamond sintered body in an acid solution to remove the iron group metal from a surface portion of the diamond sintered body and thereby make the content of the iron group metal lower in the surface portion than in an inner portion of the diamond sintered body tool, and (3) forming a surface including at least one selected from the group of silicon, a silicon oxide, a silicon carbide, a silicon nitride and a solid solution thereof on a surface of the surface treated diamond sintered body, and (4) processing the diamond sintered body on which the surface layer is formed to obtain a diamond sintered body tool.
The acid solution preferably includes at least one selected from the group of nitric acid, hydrochloric acid and hydrofluoric acid.
The content of the iron group metal in the surface portion is preferably at most 2.0% by weight.
A method of manufacturing a diamond sintered body tool according to a further aspect of the present invention includes the steps of (1) preparing a diamond sintered body, (2) forming a surface layer including at least one selected from the group of silicon, a silicon oxide, a silicon carbide, a silicon nitride and a solid solution thereof on a surface of the diamond sintered body, and (3) processing the diamond sintered body on which the surface layer is formed to form a diamond sintered body tool.